Hammond 1750L 60W Bassman Output Transformer, 4 Ohm Secondary

The 1750L is a 60 watt push-pull output transformer for tube guitar amplifiers, designed as a drop-in replacement for the original unit in the Fender Bassman, Hot Rod Deville and Concert II. It is listed as similar to Fender part numbers 022871 and 125A13A, with reference chassis numbers 5F6, 5F6A, 10, Blackface, AA864, AA165, AB165, Silverface and AA270, covering a long run of Bassman-family builds.

It matches a 4,200 ohm centre-tapped primary (brown and blue with a red centre tap) to a single 4 ohm secondary (green, with black common). Typical DC resistance is 98.6 ohms brown-blue on the primary and 0.170 ohm black-green on the secondary. At 1.0 kHz, 1.0 V open circuit, the blue-brown primary measures 6.52 H (41.6 KOhm), and primary leakage inductance is 4.93 mH.

The drawing lists a frequency response of 70 Hz to 15 kHz (0/-1.0 dB reference @ 1 kHz) and distortion of less than 2% at 70 Hz. It is paper wound, with materials and design specifications kept as close as possible to the original part to preserve the stock tone, and constructed to look similar to the factory original where possible.

Open-style construction provides 9 in minimum primary and secondary leads. Drawing dimensions are A 4.050 in, B 3.050 in reference, C 3.46 in max, D 3.500 in, E 2.490 in and F 1.940 in, with G 0.187 x 0.300 in. Ratings are 2000 VRMS dielectric strength and -40 to 105 degC. The 1750L is RoHS and REACH compliant and ships at 4 lbs (1.81 kg).